Contact tracing is a core public health tool used to interrupt the transmission of pathogens, including SARS-CoV-2. To increase the effectiveness of contact tracing, Greek health authorities used an electronic platform to aid traditional manual contact tracing to track individuals who have come in close contact with identified COVID-19 patients.

Contact tracing was implemented from the beginning of the pandemic in Greece. The aim was to identify and quarantine all the contacts of confirmed cases. The electronic database was designed following all the security protocols and national regulations on the use and protection of personal data. To assess factors associated with infectivity and susceptibility to infection in this analysis, we used contact tracing data with a sampling date between October 1 to December 9, 2020.

During the sampling period, 29,385 laboratory-confirmed SARS-CoV-2 cases and 64,608 traced contacts were identified. A median number of two persons were traced per index case. The secondary attack rate was 17.4% (95% CI: 17.0-17.8). Contacts aged 0–11 and 12–17 years were less susceptible to infection than adults 65 years or older (odds ratio (OR) [95% CI]: 0.28 [0.26–0.32] and 0.44 [0.40–0.49], respectively). Index cases aged 65 years or older were more likely to infect their contacts than other adults or children/adolescents.

Contact tracing is a key strategy to interrupt chains of transmission and to promote early diagnosis. The data collected in this process could be used to estimate epidemiological parameters of interest and to better understand factors associated with infection and susceptibility to infection. Precautions are necessary for individuals 65 or older as they have higher infectivity and susceptibility in contact with their peers.